1. Field of the Invention
The present invention relates to increasing of the size of a touch screen in a touch panel.
2. Description of the Related Art
Attention has been focused on touch panels capable of detecting touches of a pointing body such as a finger thereon and identifying the coordinates of the position thereof, as one of excellent user interface devices. Touch panels of various types, such as resistance-film types or capacitance types, have been produced.
Among these types, as one of capacitance types, there is a Projected Capacitive Touchscreen type capable of detecting touches of pointing bodies thereon, even when the touch screen incorporating touch sensors is covered at its front surface with a protective film, such as a glass plate with a thickness of about several millimeters. This Projected Capacitive Touchscreen type has the advantage that it offers excellent rigidity since a protective film can be placed on its front surface, the advantage that it is capable of detecting touches of even gloved fingers thereon, and the advantage that it has a long lifetime since there is no operating portion, and the like.
For example, a conventional touch panel of the Projected Capacitive Touchscreen type includes a touch screen including, as detection conductors for detecting capacitances, a first series of conductor elements formed on a thin dielectric layer, and a second series of conductor elements formed to be separated from the first series of conductor elements with an insulation layer interposed therebetween, such that there are spatially formed a plurality of intersection points, without inducing electric contacts among the conductor elements (refer to National Publication of Translation No. 09-511086, for example). Optimum materials of the conductor elements are metal materials, such as silver. Further, in view of display, the visibility of the conductor elements becomes a problem, and, in cases of reducing the visibility, a transparent conductive layer made of indium oxide and the like is employed as conductor elements. Also, instead of the conductor elements, thin conductor wires can be employed as detection wirings in touch panels.
Further, the conductor elements for detecting capacitances are connected to a capacitance control oscillator, through an output line and a multiplexer. A divider counts the output therefrom to create capacitance detection data.
In cases of forming the detection wirings in such a touch panel from transparent conductive layers, there is a low possibility of degradation of the quality of the display on the display device equipped with the touch panel, but there is the problem of difficulty in increasing the size of the touch panel, due to the high resistance of the transparent conductive layers forming the detection wirings.
To cope therewith, use of metal layers as detection wirings is conceived, in order to reduce the resistance of the detection wirings to realize an increase of the size of the touch panel. However, in this case, the detection wirings can be visually recognized through reflected light, thereby inducing the problem of degradation of the display quality.
Therefore, in order to reduce the resistance of the detection wirings and also to reduce the reflected light for preventing the detection wirings from being visually recognized through the reflected light for realizing an increased size of the touch panel, thin metal conducive wires are used as the detection wirings. However, in this case, if a structure including detection wirings made of thin metal conducive wires with an increased wiring density is employed for detecting the large area, this induces large parasitic capacitances among the column metal conductive wires and the row metal conductive wires, thereby inducing the problem of the occurrence of delays in wirings.
Further, in such a conventional touch panel, if the first and second series of conductor elements are made of a transparent material, it is possible to provide a touch panel with excellent viewability, but conventional transparent materials have high electric resistances, which has induced the problem of reduction of the response speed. In order to overcome this fact, there has been suggested formation of the first and second series of conductor elements from a non-transparent material with high conductivity, such as silver, but, in this case, a light-transmittance difference is induced between the portions including the detection wirings and the portions including no detection wirings, which has induced the problem of the occurrence of display unevenness due to the periodic change of the light transmittance.
Further, when such a touch panel is mounted to a display device, there has been induced the problem of the occurrence of moires due to the interference of the aforementioned periodic change of the light transmittance with the periodically-arranged pixels in the display device.